The normal cell displays intricate and coordinated interplay in the regulation of its many reactions and processes. The neoplastic cell is defective in such interplay and proliferates without differentiation. Cyclic AMP mediates the action of a wide variety of hormones and thus affects many enzymic reactions and cellular processes. The recent findings that dibutyryl cyclic AMP restores contact-inhibited growth to spontaneously and virally transformed 3T3 cells indicates that the nucleotide may have a role in the altered properties of the cancerous cells. The tissue level of cyclic AMP is controlled by the activities of adenyl cyclase which catalyzes its formation from ATP, and that of phosphodiesterase which catalyzes its hydrolysis to 5'-AMP. Any alteration in the properties of these enzymes would affect the tissue level of cyclic AMP, which will in turn affect cell growth and morphology. Adenyl cyclase and phosphodiesterase from 3T3 cells and 3T3 transformants will be characterized with special emphasis on their regulatory properties. In addition, cyclic AMP level in the two cell lines will be determined. Correlation between the tissue cyclic AMP and the activities of the two enzymes will be made. The cyclic AMP binding protein has provided us with a system to study the properties of the binding site to cyclic AMP. Future work will deal with the characterization of binding protein in the 3T3 cells and 3T3 transformants. Factors that affect the binding and the dissociation of cyclic AMP from the protein will be investigated.